While particulate desiccants such as molecular sieves are widely used in compressed gas filter assemblies for selectively adsorbing a contaminant, such as moisture, entrained in the gas, if the desiccant is not tightly compacted in the canister or other container in which it is contained, the inter-abrasion of the desiccant particles produces an abrasive dust which is carried off by the filtered product gas to the detriment of air brakes or other devices operated by the product gas. Fluid-actuated top or bottom-acting compactors, such as disclosed in the filter assemblies of Lanier Frantz U.S. Pat. No. 4,029,086 and my U.S. Pat. No. 4,113,451, by exerting a compacting force on the desiccant, minimize dust formation by the desiccant particles. Also, as opposed to the external compacting springs they are designed to replace, the fluid-actuated compactors of the Frantz patents not only automatically apply a substantially uniform force over their compacting range but can readily release that force to facilitate insertion and removal of the canister.
Necessarily limited in their automatic compacting action to a particulate desiccant in a canister installed in a filter assembly, the disclosed embodiments of the compactors of the Frantz patents cannot compensate for any looseness of the desiccant charge before the canister is installed and, given such looseness, the handling of a charged canister before installation, particularly in the field, can cause the desiccant particles to create dust. If, as in those patents, the canister closure is rigid, avoidance of the initial looseness requires that the canister be very carefully loaded to capacity and this in turn renders it difficult to apply the closure. It is to a solution of these problems that the present invention is particularly directed.